1. Field of the Invention
The invention relates to a new process for the treatment of heat-sensitive materials, particularly foodstuffs, which involves the intimate contacting of plural, distinct physical phases and the ultimate separation of the various products resulting therefrom.
2. Description of the Prior Art:
The drying and dehydration of heat-sensitive substances, particularly food products, have been the subject of numerous studies and publications. Thus, as early as 1906, U.S. Pat. No. 860,929 proposed elimination of moisture from liquid, semi-liquid or solid materials to afford dry products, by pulverizing the mass and contacting it with a flow of cold or hot air. This process was recommended for drying juice, pulps, milk, eggs and medicines, but it had two major disadvantages. First, it was performed in an uncertain manner, from volume element to volume element, which caused the treatment time to vary from one element to another. Thus, in order to be reasonably certain that all of the material had been treated, the retention time of the phases had to be extended. This first disadvantage entailed a second one, namely the necessity of utilizing a gas for the treatment at a temperature near that of the product to be treated, in order not to run the risk of degrading the product. This resulted on the one hand in a poor distribution of the characteristics of the product obtained and, on the other, in a poor thermal yield. Nevertheless, for a long period of time the processes of contacting the treating substances with the substances to be treated rested on the principle of the uncertain distribution of contacts, in the absence of a knowledge of how to achieve organized distribution.
An ideal spray dryer which would eliminate the disadvantages indicated above would comprise a vertical, cylindrical contact zone in which the gas and the dispersed liquid droplets are uniformly, regularly distributed, with the liquid being dispersed or entrained therein in the form of substantially equally sized droplets. Ideally, all of the droplets would follow the same flow path through the apparatus as to be subjected to the same treatment and, accordingly, to continuously give rise to the formation of identical product. Stated differently, the entire volume of the physical phase to be treated, in this spray drying event the same being a dispersed liquid droplet phase, should be subjected to the same historical profile operationally in order to receive an essentially identical amount and duration of treatment by the treatment medium or phase, under the same conditions (especially those of temperature and concentration). And the immediately aforesaid of course presupposes or implies the realization or attainment of a precisely, indeed near perfectly controlled rate of flow.
In our abandoned application, Ser. No. 770,802, filed Feb. 22, 1977 (a continuation of our abandoned parent application, Ser. No. 479,774, filed June 17, 1974), it has been shown that certain conditions very close to the ideal can be attained by insuring flow or distribution of vortex type, by operating within certain well defined parameters of both geometry and kinetics. As disclosed in the noted '802 application (heavy expressly incorporated by reference in its entirety and relied upon), in an initial stage in the process the plural phases are manipulated upstream of their convergence by supplying same to a cylindrical distribution zone, at least one of the phases being introduced via a helical trajectory inducing inlet and being axially extended, while maintained in an axially symmetrical, helical flow path, through said distribution zone. By "axially symmetrical, helical flow path", there is denoted a regularly repeating, helical path of axially extending downward flow which is essentially symmetrical with respect to at least one plane containing the axis of such helical flow. At least one other phase is also introduced to the distribution zone, via a suitable inlet and it too is axially extended therethrough, but in this instance the path of downward flow is essentially rectilinear. The longitudinal axis of the path of rectilinear flow is, moreover, coaxial with the longitudinal axis of the path of helical flow. The current of circulating helical flow next progresses to a confining zone of restricted flow passage so constructed that the minimum momentum of the helical flow is at least 100 times greater than the momentum of the coaxial rectilinear flow, and such that the plural flow paths or separately supplied phases converge and are combined, blended and admixed in yet a third distinct zone, the contact zone. Thus, the trajectory imparted by the helical flow, at its point of exit from the zone of restricted flow passage, forms one of the classes of generatrices of a hyperboloid to a thin surface, or, more correctly, a layered stack of a plurality of hyperboloids. Said generatrices are conveyed through a series of circles to form a ring of narrow width which is situated downstream of the restricted passage for the helical flow, but upstream of its divergence. This ring surrounds a zone of depression, the effects of which are manifested both upstream, on the phase constituting rectilinear flow, as well as downstream, on the phase constituting circulating helical flow, by effecting the recycling of a portion of such fluids. In this fashion, in the zone downstream from the area of combining or convergence of the separately supplied fluids or plural flow paths, and in the same plane which is perpendicular to their coaxis, all vectors of the individual elements constituting total volume are equal in absolute value, are divergent and are mutually subtracted upon rotation about the coaxis; hence, at two successive intervals, two distinct units of volume in the same trajectory evidence the same historical processing profile, thus assuring maintenance of contact between the two phases. Accordingly, if the rectilinear flow, for example, be constituted of a liquid phase and the helical flow of a gaseous phase, the liquid phase will be disintegrated, fractionated or atomized into a multitude of droplets, with each droplet being dispersed in a given volume of the gas and subjected to a certain movement or velocity thereby, by being physically swept along with said gas, thus creating the effect of centrifugation; this phenomenon enhances contact with the vector gas and, in those cases where combustion results, insures ignition and flame stability. Such a process, therefore, in a notably marked advance in the art of rapid intimate contact between two disparate phases. Nonetheless, a product separation problem arises, for example, the elimination of gases from any solid or liquid phase recovered. In Ser. No. 770,802, this function of separation is assured by means of a cyclone.
Thus, in Ser. No. 770,802, the same means perform the uniform formation of the dispersion and its equally uniform treatment from volume element to volume element. In a simple manner, it may therefore be said that the system acts as a piston and as a flash reactor at the same time. Because of this dual character, it is possible to treat uniformly and in a very short period of time, heat-sensitive materials with gases at a temperature higher than could ordinarily be endured by said materials, since the true temperature to be taken into consideration is that, not of the gaseous phase performing the treatment, but that actually attained by the substance being treated.
The process of Ser. No. 770,802 has yielded excellent results. However, it is clear that the time of treatment, reduced to the distance through the piston zone of flow, is very short. In this part of the apparatus, the release of moisture is thus very great and the resulting downstream environment has a moisture content which, in the vicinity of the walls, is difficult to control. This difficulty is enhanced by the fact that the substances are not immediately separated and collected, the separation being generally effected by a cyclone following and downstream of the vessel in which contact takes place. To reduce this problem (as well as to avoid disadvantages inherent in the use of a cyclone to achieve separation), our abandoned application, Ser. No. 872,151, filed Jan. 25, 1978 provides a cylindrical wall member integrally secured to the trajectories or outlet of the contact zone of any device disclosed in our abandoned application, Ser. No. 770,802, effecting an abrupt change or variation in the velocity field of at least one of the phases, while at the same time maintaining the general direction of flow of said phases. More particularly, according to the invention of Ser. No. 872,151, there are provided both apparatus and process for the formation of an intimate, homogeneous product mix comprising at least two disparate physical phases, and for the ultimate facile separation and recovery of the various products resulting from such mixing. According to the '151 invention an intimate, homogeneous admixture of said phases is assured by mutually contacting the same by means of a flow of vortex type. This is accomplished by supplying at least one of the phases to a first cylindrical distribution zone via a helical trajectory inducing inlet, and whereby the same is axially extended through such zone while being maintained in an axially symmetrical, helical flow path. By "axially symmetrical, helical flow path", here too is intended a regularly repeating, helical path of axially extending downward flow which is essentially symmetrical with respect to at least one plane containing the axis of the helical flow. At least one other phase is also introduced to this first distribution zone, via a suitable inlet, and it too is axially extended therethrough, but in this instance the path of downward flow is essentially rectilinear. The longitudinal axis of the path of rectilinear flow is, moreover, coaxial with the longitudinal axis of the path of helical flow. The current of circulating helical flow next progresses to a confining zone of restricted flow passage so constructed that the minimum momentum of the helical flow is at least 100 times greater than the momentum of the coaxial rectilinear flow, and such that the plural flow paths or separately supplied phases converge and are combined, blended and admixed in yet a third distinct zone, the contact zone. In the contact zone, the trajectories common to the different phases are directed against a cylindrical surface, the intimate admixture remaining in contact with said surface as a result of the effects of that centrifugal force imparted to the system by means of the circulating, helical flow. Phase separation is next effected by an abrupt change in the field of velocities of at least one of the disparate phases, while at the same time maintaining the general direction of flow of the several phases. Ultimately, the products resulting from the intimate admixture or contacting of the various phases are recovered separately. The plural phases subjected to treatment according to the '151 invention may be either gaseous, liquid or solid phases. Typically, the kinetics of the procedure according to the '151 invention are tantamount to those described in our aforesaid application, Ser. No. 770,802, namely, the minimum momentum of the helical flow is at least 100 times greater than the momentum of the coaxial rectilinear flow.
The abrupt change or variation in the field of velocities of at least one of the disparate phases is conveniently and practically achieved by mere abrupt change in the direction of the helical flow. The abrupt change in direction may also be effected by substantial variation in the cross section of the downstream zone of cylindrical flow. Also, if a particular treatment be carried out according to the '151 invention, such as, for example, a concentration, yet another treatment or processing parameter may be added thereto or combined therewith, e.g., an additional thermal or chemical treatment; any thermal treatment may be effected by a given phase, per se.
The apparatus according to the '151 invention may easily be fabricated, simply by adding or securing to the contactor disclosed in the noted '802 application, (1) a vertical, cylindrical wall member integral therewith and axially downstream therefrom and in communicating relationship therewith, and defining a phase separation zone, (2) a base member, said base member having a cross section which is greater in diameter than the diameter of the cylinder (1) defining the phase separation zone, and also being integral and in communicating relationship therewith, said base member comprising (3) an outlet or evacuating conduit for the lightest of the plural phases, with the upstream or inlet end of such conduit or duct being disposed essentially planar with, or at the height of the point of integral junction between the cylindrical wall member (1) and the base member (2). The angle of juncture between the cylindrical wall member and the base member having the greater diameter cross section may vary over considerably wide limits.
In another embodiment of the '151 invention, apparatus otherwise identical to that immediately above-described may be utilized, except that the base member may itself have a cross section which is identical to that of the vertical, cylindrical wall member. The base member may be, for example, itself cylindrical, in which case it can be directly, integrally attached to the cylindrical wall member by means of any suitable sleeve, but the same may also be of slightly greater or lesser cross section and thus directly integrally attached to the cylindrical wall member, for example, by force-fit, suitable gasket and nuts and bolts, or other securing means.
The contactor of the '151 invention too may be comprised of a variety of other elements, such as one or more hoppers and various conduits defining both inlets and outlets for the introduction and removal of the various plural phases. For the sake of simplicity and brevity, that device according to the abandoned application, Ser. No. 770,802, shall hereinafter be referred to as the "head" of the subject contactor. Such a head conveniently comprises an at least partially cylindrical casing or tubular wall member terminating at its downside end either (i) in a truncated cone, the smaller base of which defining the downstream outlet of the distribution zone (as well as defining the confining zone of restricted flow passage), or (ii) terminating in a centrally apertured flat disc or plate, said central aperture being both circular and coaxial with the casing or tubular wall member. The circular aperture, in this embodiment, also defines the confining zone of restricted flow passage. The upstream end of the casing or tubular wall member is sealed, but has extending therethrough and deep within the casing an internal conduct or pipe member which is coaxial with the tubular casing, and which terminates in an outlet aperture which is spaced from the mean plane of the circular aperture defining the confining zone of restricted flow passage by a length or distance which is between 0 and the radius of said zone of restricted flow passage. The head also comprises a helical trajectory inducing inlet for one of the phases, and means for axially extending the flow from such inlet completely through that interspace thus established between the inner walls of the tubular casing and the outer walls of the coaxial, internal tubular conduit, while at the same time being maintained in an axially symmetrical, helical flow path.
The coaxial, internal tubular conduit or pipe may inself envelop yet one or more additional coaxial, concentric tubular conduits, for example, where necessary to rectilinearly charge several fluids which should be kept out of mutual contact or admixture with each other prior to their contact or admixing with the helical flow current.
It is, nonetheless, highly essential that the helical flow be maintained axially symmetrical, i.e., a regularly repeating, helical path of axially extending downward flow which is essentially symmetrical with respect to at least one plane passing through the axis of the helical flow. In the case of a contactor having relatively small dimensions, this object is conveniently attained by utilizing more than one helical trajectory inducing inlet, but, advantageously, the wall member defining the first distribution zone simply comprises a perforated, at least partially cylindrical or frusto-conical element fitted within an outside enveloping continuous jacket adapted to, and receiving a tangential, helical trajectory inducing inlet. The apertures or orifices comprising such an element are necessarily "thin-walled orifices". It too is important that the distribution of such orifices or apertures be regular and that the surface area of the orifices be such that the perforate wall, in the majority of cases, does not induce a pressure drop of greater than about 50 g/cm.sup.2 in the fluid flow; a flow rate of 35 m.sup.3 /h through an aperture 20 mm in diameter, for example, is easily obtainable. Cf. our abandoned application, Ser. No. 770,802.
In a particularly advantageous embodiment according to the '151 invention, the diameter of the outlet or evacuating conduit comprising the base member is at least two thirds of the diameter of the cylindrical wall member defining the phase separation zone.
Thus, Ser. No. 872,151 (hereby expressly incorporated by reference and relied upon) provides excellent phase separation. However, this solution is not always satisfactory in itself because the nature of the environment and its physical conditions are not changed and the problem of excess moisture remains.